24.5. Avoiding Race Conditions by Synchronizing with Signals

After a fork(), if either process needs to wait for the other to complete an action, then the active process can send a signal after completing the action; the other process waits for the signal.

Example 24-6 demonstrates this technique. In this program, we assume that it is the parent that must wait on the child to carry out some action. The signal-related calls in the parent and child can be swapped if the child must wait on the parent. It is even possible for both parent and child to signal each other multiple times in order to coordinate their actions, although, in practice, such coordination is more likely to be done using semaphores, file locks, or message passing.